The present invention is directed to a hydraulic power system having two or more hydraulic power converters in which it is desired that the speed of one of the power converters changes proportional to the speed of another power converter.
It is well known that in many hydraulic power applications, it is very desirable and often imperative to link the speed of one hydraulic converter to the speed or feed rate of another hydraulic converter or actuator. For example, in a sawing application where a circular saw blade is driven by a rotary hydraulic converter or motor and a linear hydraulic actuator is used to feed the circular saw blade into the material to be cut, it is necessary to regulate the feed rate of the saw with the rotary speed of the saw. If the saw blade slows down and the feed rate is unchanged, then the saw blade can stall because the teeth of the blade are forced to take larger and larger bites per pass through the material.
Another example of the desirability of tying the feed rate to the speed of rotational motion is in the mining industry where roof bolt drilling is being performed. A drill bit being rotated by a rotary hydraulic converter is fed into the roof of a mine by a hydraulic linear actuator. It is very desirable to regulate the feed rate of the drill to the speed of the drill. In addition, drill rate can be improved and bit life improved if the feed rate can be oscillated; this can be accomplished by quickly increasing, then decreasing, the flow of fluid to the hydraulic linear actuator.
A third example of the desirability of linking the speed of two or more hydraulic converters is present in conveyor drives, where the speed of one rotary hydraulically powered conveyor can be tied to the speed of another conveyor. When one conveyor is heavily loaded, it will slow down when compared to a lightly loaded conveyor; this is so because the pressure of the fluid in the hydraulic converter heavily loaded is higher than the pressure in the converter of the lightly loaded conveyor; the higher pressure causes an excess of internal leakage in the hydraulic converter carrying a heavier load.